1. Field of the Invention
The present invention relates to a bearing apparatus having a rotator body and a non-rotation body in which the rotator body is supported in a thrust direction by a thrust dynamic pressure generated between thrust bearing surfaces of the rotator body and the non-rotation body, which is applicable as, for example, a bearing apparatus of a hard disc drive motor, and a variety of optical disc drive motors.
2. Description of Related Art
A variety of strict demands in higher accuracy at higher speeds, longer service life, and lower noise are imposed on small size spindle motors that are used for hard disc drive apparatuses and various optical disc drives. To meet the demands, it is effective to make bearing apparatuses with dynamic pressure bearings. In this connection, a bearing apparatus in which its radial bearing and thrust bearing are both formed by dynamic pressure bearings has been developed.
A typical dynamic pressure bearing uses a lubrication fluid filled in a minute gap between a rotator body and a non-rotation body and generates a pressure by a shearing force caused by the lubrication fluid to support the rotator body in a non-contact manner. Therefore, it is essential to work parts at a high level of precision and assemble them at a high level of precision in order to provide and maintain a minute gap between the rotator body and the non-rotation body.
With high precision machine tools, a radial dynamic pressure bearing can be relatively readily manufactured with high precision, and its required assembly accuracy can be relatively readily achieved. However, for a thrust dynamic bearing, much strict accuracy is required since a flange shaped thrust plate needs to be assembled on a rotator shaft, and a level of precision in the order of xcexcm needs to be secured in the assembly work. Also, since a thrust dynamic bearing supports the weight in the direction of gravity, the rotator body may often contact the non-rotation body when the rotation is stopped, which results in shortening the service life of the bearing apparatus, and also the service life of the motor.
To solve the problems described above, a bearing apparatus is provided with a radial bearing that is formed from a dynamic pressure bearing and a thrust bearing that is formed from a magnetic bearing.
However, the thrust bearing formed from a magnetic bearing has the following problems.
When the magnetic bearing is a controlled type to maintain the position of the rotator body in its axial direction constant, electric power needs to be constantly supplied. As a result, the motor suffers a large amount of losses.
Since the magnetic force is relatively small compared to the dynamic pressure, the rotator body would likely contact the non-rotation body by impact forces.
Since the magnetic force is relatively small compared to the dynamic pressure, the bearing apparatus tends to become larger in size to obtain a predetermined supporting force in the thrust direction.
Since the magnetic bearing has a lower dynamic rigidity compared to the dynamic pressure bearing, it is rather vulnerable to high frequency vibrations compared to the dynamic pressure bearing.
The present invention has been made to solve the problems of the conventional art describe above.
It is an object of the present invention to provide a bearing apparatus having an active magnetic bearing that requires electrical power that is used only to control vibration components. As a result, the bearing apparatus in accordance with the present invention reduces the power consumption, securely prevents contacts between a rotator body and a non-rotation body and substantially extends the service life of the bearing apparatus.
It is another object of the present invention to provide a bearing apparatus that may include a thrust dynamic pressure bearing and an active magnetic bearing provided in combination such that characteristics of the respective bearings are effectively used. For example, the static rigidity is born by the active magnetic bearing and the dynamic rigidity is born by the dynamic pressure bearing. As a result, the bearing apparatus has a higher accuracy and a longer service life and can reduce the load torque at the time of starting its rotation, compared to a bearing apparatus that uses only a thrust dynamic pressure bearing or an active magnetic bearing.
It is still another object of the present invention to provide a bearing apparatus that may include a thrust dynamic pressure bearing and an active magnetic bearing used in combination. In one aspect of the present embodiment, the load applied to the dynamic pressure bearing is reduced compared to a bearing apparatus that uses only a dynamic pressure bearing, the distance of a fine gap that forms the dynamic pressure bearing can be made relatively large, the need to strictly manage the working precision and assembly accuracy for parts of the dynamic pressure bearing can be eliminated, and the manufacturing cost is lowered.
In accordance with an embodiment of the present invention, a bearing apparatus includes a rotator body, a non-rotation body rotatably supporting the rotator body, and a lubrication fluid present between the rotator body and the non-rotation body in which the rotator body is supported in a thrust direction by a thrust dynamic pressure bearing formed between the rotator body and the non-rotation body. The bearing apparatus comprises an active magnetic bearing formed by a driving coil disposed on one of the rotator body and the non-rotation body and a magnet disposed on the other thereof, and a gap sensor that detects an axial direction gap between the rotator body and the non-rotation body, wherein the axial direction gap is controlled by controlling current applied to the driving coil based on an output of the gap sensor.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.